Also, it was clear that Dot was always going to be one of those journeymen officers who never rise because they're lazy and thick.
It's one of the reasons he's not suspected of complicity in the murders of the drug dealers. He's assigned to watch their flat but skived off. It's the kind of thing he would do. Except you find out that he did it deliberately.
I can't remember his rank - not above DS.
Gates was very ambitious and gifted and the Morrissey character was a good policeman but with no drive.
Dot lucks in on his promotion at the end. It's interesting because that happens quite a lot, as another poster has said. Inept people do get lucky. It's quite depressing.